Electrophoretic imaging process using photosensitive xanthenonium salts



March 11, 1969 s. s. LABANA 3,432,415

ELECTROPHORETIC IMAGING PROCESS USING PHOTOSENSITIVE XANTHENONIUM SALTSFiled Oct. 1, 1965 INVENTOR. SANTOKH S. LABANA Bvwww United StatesPatent 19 Claims This invention relates in general to imaging methods.More specifically, the invention concerns the use of electricallyphotosensitive particles in electrophotographic imaging systems.

There has been recently developed an electrophoretic imaging systemcapable of producing color images which utilize photoconductiveparticles. This process is described in detail and claimed in copendingapplications Ser. Nos. 384,737, 384,681, now abandoned, and 384,680, nowabandoned, all filed July 23, 1964. In such an imaging system, variouscolored light absorbing particles are suspended in a non-conductiveliquid carrier. The suspension is placed between electrodes, subjectedto a potential difference and exposed to an image. As these steps arecompleted, selective particle migration takes place in imageconfiguration, providing a visible image at one or both of theelectrodes. An essential component of the system is the suspendedparticles which must be intensely colored and electricallyphotosensitive and which apparently undergo a net change in chargepolarity upon exposure to activating radiation, through interaction withone of the electrodes. The images are produced in color because mixturesof two or more differently colored sets of particles which are eachsensitive only to light of a specific wavelength or narrow range ofwavelengths are used. Particles used in this system must have bothintense pure colors and be highly photosensitive. The materials of theprior art often lack the purity and brilliance of color, the high degreeof photosensitivity, and/ or the preferred correlation between the peakspectral response and peak photosensitivity necessary for use in such asystem.

Another imaging system .which utilizes electrically photosensitivematerial is the xerographic process as described in US. Patent 2,297,691to C. F. Carlson. Here, the photosensitive material must be an effectivephotoconductive insulator, i.e., must be capable of holding anelectrostatic charge in the dark and dissipating the charge to aconductive substrate when exposed to light. In the fundamental process,a base sheet of relatively low electrical resistance such as metal,paper, etc., having a photoconductive insulating surface coated thereon,is electrostatically charged in the dark. The charged coating is thenexposed to a light image. The charges leak off rapidly to the base sheetin proportion to the intensity of light to which the particular area isexposed, the charge being substantially retained in nonexposed areas,forming an electrostatic latent image. After exposure, the coating iscontacted with electrostatic marking particles in the dark. Theseparticles adhere to the areas where the electrostatic charge remains,forming a powder image corresponding to the electrostatic latent image.Where the base sheet is relatively inexpensive, such as paper, the imagemay be fixed directly to the plate, as by heat or solvent fusing.Alternatively, the powder image may be transferred to a sheet oftransfer material, such as paper, and fixed thereon.

Patented Mar. 11, 1969 ice Many photosensitive materials useful in thexerographic process are known in the art, e.g., vitreous selenium,sulfur, anthracene, zinc oxide, polyvinyl carbazole. While several ofthese different materials are in commercial use today, each hasdeficiencies in such areas as photographic speed, spectral response,durability, reusability and cost such that there is a continuing needfor improved materials.

It is, therefore, an object of this invention to provideelectrophotographic imaging processes which overcome the above noteddeficiencies.

It is another object of this invention to provide novel electrophoreticimaging processes.

It is still another object of this invention to provide novelelectrophoretic imaging systems capable of repro ducing color images.

It is still another object of this invention to provide novelxerographic plates having maximum spectral and photosensitive responsesin ranges other than those of prior plates.

The foregoing objects and others are accomplished in accordance withthis invention, fundamentally, by providing novel electrophotographicimaging processes utilizing a lake of a3,6-bis(amino)-9,2'-carboxyphenyl xanthenonium salt.

The compositions within the general formula given above are derivativesof 9-phenylxanthene containing alkylamino or arylarnino groups andbelong to the class of metal oxide lakes obtained from N-substituted3,6bis- (amino)-9,2-canboxyphenyl xanthenonium chloride. Typicalcompositions within this class are: phosphotungstomolybdic lake obtainedfrom 3,6-bis(ethylamino)-9,2-carboxyphenyl xanthenonium chloride (bluishred), phosphotungstomolybdic lake obtained from 3,6-bis(et -hylamino)9,2 carbethoxyphenyl xanthenonium chloride (bluish pink),phosphomolybdic lake obtained from 3,6- bis(ethylamino) 2,7dimethyl-9,2-carbethoxyphenyl xanthenonium chloride (bluish red), sodiumsalt of 3,2- toluidine amino-6,2"-methyl-4"-sulphophenylamino-9,2"-carboxyphenyl xanthene (violet), phosphotungstomolybdic lake obtainedfrom 3,-6-bis(diethyla-mino)-9,2'-car bethoxyphenyl xanthenoniumchloride (reddish violet), phosphotungstomolybdic lake obtained from3,6-bis(diethylamino)-9-(2,5-dicarboxy 4 hydroxyphenyl)xanthene (bluishred), barium salt of 3,2'-toluidine amino- 6,2"methyl-4"sulphophenylamino-9,2"-carboxyphenyl xanthene (reddish violet)and mixtures thereof.

These compositions may be prepared by condensing two moles ofm-dialkylaminophcnol with phthalic anhydride by heating to a hightemperature (about 200 C.) in the absence of any condensing agent. Ifdesired, a condensing agent, such as sulfuric acid may be used. The dyethus produced is then precipitated with a suitable metallic compound(e.g., sodium phosphotungstate and phosphomolybdic acid) to form therelatively insoluble lake. Any conven'ional synthesis may be used toprepare the compounds of the above general formula. For example, themethods described in German Patents 403,- 002 and 449,539 may be used.

Of the compositions within the general formula given above, thephosphotungstomolybdic lake and barium salt of 3 ,6-bis diethylamino-9,2'-carboxyphenyl xanthenonium chloride, the phosphomolybdic lakeobtained from 3,6 bis(ethylamino)2,7-dimethyl-9,2'-carbethoxyphenylxanthenonium chloride and the barium salt of 3,2'-toluidineamino-6,2"-methyl-4"-sulphophenylamino-9,2-carboxyphenyl xanthene arepreferred for use in electrophoretic imaging processes since they aresimply and economically synthesized, have especially desirable color andhave high electrical photosensitivity. Of these, the optimum compositionis the phosphomolybdic lake obtained from3,6-bis(ethylamino)-2,7-dimethyl-9,2'-carbethoxyphenyl xanthenoniumchloride. Since the shade or tone of the compositions and the spectraland photosensitive responses vary slightly depending upon thesubstituent used, intermediate values of these variables may be obtainedby mixing several of the different compositions.

The compositions within the general formula listed above, and mixturesthereof, are especially useful as photosensitive pigment particles inelectrophoretic imaging processes. An exemplary electrophoretic imagingsystem is shown in the figure.

Referring now to the figure, there is seen a transparent electrodegenerally designated 1 which, in this exemplary instance, is made up ofa layer of optically transparent glass 2 overcoated with a thinoptically transparent layer 3 of tin oxide, commercially available underthe name NESA glass. This electrode will hereafter be referred to as theinjecting electrode. Coated on the surface of the injecting electrode 1is a thin layer 4 of finely divided photosensitive particles dispersedin an insulating liquid carrier. The term photosensitive, for thepurposes of this application, refers to the properties of a particlewhich, once attracted to the injecting electrode, will migrate away fromit under the influence of an applied electric field when it is exposedto actinic electromagnetic radiation. For a detailed theoreticalexplanation of the apparent mechanism of operation of the invention, seethe above mentioned .copending applications Ser. Nos. 384,737, 384,681and 384,680, the disclosures of which are incorporated herein byreference. Liquid suspension 4 may also contain a sensitizer and/or abinder for the pigment particles which is at least partially soluble inthe suspending or carrier liquid as will be explained in greater detailbelow. Adjacent to the liquid suspension 4 is a second electrode 5,hereinafter called the blocking electrode, which is connected to oneside of the potential source 6 through a switch 7. The opposite side ofpotential source 6 is connected to the injecting electrode 1 so thatwhen switch 7 is closed, an electric field is applied across the liquidsuspension 4 between electrodes 1 and 5. An image projector made up of alight source 8, a transparency 9, and a lens 10 is provided to exposethe dispersion 4 to a light image of the original transparency 9 to bereproduced. Electrode 5 is made in the form of a roller having aconductive central core 11 connected to the potential source 6. The coreis covered with a layer of a blocking electrode material 12, which maybe Baryta paper. The pigment suspension is exposed to the image to bereproduced while a potential is applied across the blocking andinjecting electrodes by closing switch 7. Roller 5 is caused to rollacross the top surface of injecting electrodes 1 with switch 7 closedduring the period particles originally attracted to electrode 1 tomigrate through the liquid and adhere to the surface of the blockingelectrode leaving behind a pigment image on the injecting electrodesurface which is a duplicate of the original transparency 9. Afterexposure, the relatively volatile carrier liquid evaporates off, leavingbehind the pigment image. This pigment image may then be fixed in placeas for example, by placing a lamination over its top surface or byvirtue of a dissolved binder material in the carrier liquid such asparaffin wax or other suitable binder that comes out of solution as thecarrier liquid evaporates. About 3% to 6% by weight of parafiin binderin the carrier has been found to produce good results. The carrierliquid itself may be paraffin wax or other suitable binder. In thealternative, the pigment image remaining on the injecting electrode maybe transferred to another surface and fixed thereon. As explained ingreater detail below, this system can produce either monochromatic orpolychromatic images depending upon the type and number of pigmentssuspended in the carrier liquid and the color of light to which thissuspension is exposed in the process.

Any suitable insulating liquid may be used as the carrier for thepigment particles in the system. Typical carrier liquids are decane,dodecane, N-tetradecane, paraffin, beeswax or other thermoplasticmaterials, Sohio Odorless Solvent 3440 (a kerosene fraction) andIsopar-G (a long chain saturated aliphatic hydrocarbon). Good qualityimages have been produced with voltages ranging from 300 to 5,000 voltsin the apparatus of the figure.

In a monochromatic system, particles of a single composition aredispersed in the carrier liquid and exposed to a black-and-white image.A single color image results, corresponding to conventionalblack-and-white photography. In a polychromatic system, the particlesare selected so that those of different colors respond to differentwavelengths in the visible spectrum corresponding to their principalabsorption bands. Also, the pigments should be selected so that theirspectral response curves do not have substantial overlap, thus allowingfor color separation and subtractive multicolor image formation. In atypical multicolor system, the particle dispersion should include cyancolored particles sensitive mainly to red light, magenta particlessensitive mainly to green light and yellow colored particles sensitivemainly to blue light. When mixed together in a carrier liquid, theseparticles produce a black appearing liquid. When one or more of theparticles are caused to migrate from base electrode 11 toward an upperelectrode, they leave behind particles which produce a color equivalentto the color of the impinging light. Thus, for example, red lightexposure causes the cyan colored pigment to migrate, leaving behind themagenta and yellow pigments which combine to produce red in the finalimage. In the same manner, blue and green colors are reproduced byremoval of yellow and magenta, respectively. When white light impingesupon the mix, all pigments migrate, leaving behind the color of thewhite or transparent substrate. No exposure leaves behind all pigmentswhich combine to produce a black image. This is an ideal technique ofsubtractive color imaging in that the particles are not only eachcomposed of a single component but, in addition, they perform the dualfunctions of final image colorant and photosensitive medium.

It has been found that the compounds of the general formula given aboveare surprisingly effective when used in either as single or multicolorelectrophoretic imaging system. Their good spectral response and highphotosensitivity result in dense, brilliant images.

Any suitable different colored photosensitive pigment particles havingthe desired spectral responses may be used with the pigments of thisinvention to form a pigment mix in a carrier liquid for color imaging.From about 2 to about 10 percent pigment by weight have been found toproduce good results. The addition of small amounts (generally rangingfrom 0.5 to 5 mol percent) of electron donors or acceptors to thesuspensions may impart significant increases in system photosensitivity.

The following examples further specifically define the present inventionwith respect to the use of the compositions of the general formula givenabove in electrophoretic imaging processes. Parts and percentages are byweight unless otherwise indicated. The examples below are intended toillustrate various preferred embodiments of the electrophoretic imagingprocess of the present invention.

All of the following Examples I-XI are carried out in an apparatus ofthe general type illustrated in the figure with the imaging mix 4 coatedon a NESA glass substrate through which exposure is made. The NESA glasssurface is connected in series with a switch, a potential source, andthe conductive center of a roller having a coating of Baryta paper onits surface. The roller is approximately 2 /2 inches in diameter and ismoved across the plate surface at about 1.45 centimeters per second. Theplate employed is roughly 3 inches square and is exposed with a lightintensity of 8,000 foot candles as measured on the uncoated NESA glasssurface. Unless otherwise indicated, 7 percent by weight of theindicated pigments in each example are suspended in Sohio OdorlessSolvent 3440 and the magnitude of the applied potential is 2500 volts.All pigments which have a relatively larger particle size as receivedcommercially or as made are ground in a ball mill for 48 hours to reducetheir size to provide a more stable dispersion which improves theresolution of the final images. The exposure is made with a 3200 K. lampthrough a 0.30 neutral density step wedge filter to measure thesensitivity of the suspensions to white light and then Wratten filters29, 61 and 47b are individually superimposed over the light source inseparate tests to measure the sensitivity of the suspensions to red,green, and blue light, respectively.

EXAMPLE I About 7 parts of the phosphomolybdic lake obtained from 3,6bis(ethylamino)-2,7-dimethyl-9,2'-carbethoxyphenyl xanthenonium chlorideis suspended in about 100 parts Sohio Odorless Solvent 3440. The mixtureis coated on the NESA glass substrate and a negative potential isimposed on the roller electrode. The plate is exposed through a Wrattenfilter 29 and the neutral density step wedge filter, thus exposing theplate to red light, The pig- 6 EXAMPLE v A series of tests is run as inExample I above, except that the pigment here is thephosphotungstomolybdic lake of 3,6bis(diethylamino)-9,2'-carbethoxyphenyl xanthenonium chloride. Theroller electrode is held at a negative potential. The pigment here issensitive to green and white light, but has relatively low photographicspeed. Results are tabulated in Table I below.

EXAMPLE VI A series of tests is run as in Example V above except thatthe roller electrode is held at a positive potential. The pigment isfound to have significantly higher photographic speed with positiveroller electrode potential. See Table for results.

EXAMPLE VII A series of tests is run as in Example I above except thatthe pigment here is the barium salt of3,6-bis(diethylamino)9,2'-carboxyphenyl xanthenonium chloride. Theroller is held at a negative potential. The pigment is found to besensitive to green and white light, through having low photographicspeed. See Table I for results.

EXAMPLE VIII A series is run as in Example VII above, except that theroller electrode is held at a positive potential. The pigment is foundto have substantially the same characteristics with positive or negativeroller potential. See Table I for results.

TABLE I Photographic speed (it. c.)

rum!- Green Blue White EXAMPLE II A series of tests is run as in ExampleI above, except the roller electrode here is maintained at a positivepotential. Again, the pigment is found to be relatively insensitive tored and blue light but sensitive to green and white light. However, thepigment is not as sensitive with positive roller potential as withnegative roller potential. See Table I for results.

EXAMPLE III A series of tests is run as in Example I above, except thatthe pigment here is the photophotungstomolybdic lake of 3,6bis(diethylamino) 9,2 carboxyphenyl xanthenonium chloride. The blockingelectrode is held at a negative potential. The results are tabulated inTable I below.

EXAMPLE IV A series of tests is run as in Example III above except thatthe roller electrode is held at a positive potential. This pigment isfound to have higher photographic speed with a positive roller potentialthan with negative potential. See Table I for results.

The electrophoretic sensitivity of the various pigments to red, green,blue and white light is tested according to conventional photographicmethods and the results are recorded in Table I, above. In the table,the first column lists the number of the test example. The second columngives the positive or negative electrical potential applied to theroller electrode in volts. Columns 3-6 give the photographic speed forthe tested pigment in footcandles for red, green, blue and white light.The photographic speed is the result of a curve of optical densityplotted against the logarithm of exposure in foot-candles; ft.-c. being0.3 gamma toe speed and ft.-c. being 0.3 gamma shoulder speed. Gamma, aslisted in column 7, is a standard photographic term referring to theslope of the above mentioned curve. The maximum and minimum reflectiondensity produced are listed in columns 8 and 9, respectively. As shownby the above table, the tested pigments are sensitive, in anelectrophoretic sense, to green light only. As can be seen, the pigmentsare essentially non-responsive to red and blue light. Thus, the responseto these pigments to white light is essentially identical to theirresponse to green light.

In each of Examples IX-XI below, a suspension including equal amounts ofthree different colored pigments is made up by dispersing the pigmentsin finely divided form in Sohio Odorless Solvent 3440 so that thepigments constitute about 8% by weight of the mixture. This mixture maybe referred to as a trimix. The mixtures are individually tested bycoating them on a NESA glass substrate and exposing them as in Example Iabove, except that a multicolor Kodachrome transparency is interposedbetween the light source and the plate instead of the neutral densityand Wratten filters. Thus, a multicolored image is projected on theplate as the roller moves across the surface of the coated NESA glasssubstrate. A Baryta paper blocking electrode is employed and the rolleris held at a negative potential of about 2500 volts with respect to thesubstrate. The roller is passed over the substrate six times, beingcleaned after each pass. Potential application and exposure are bothcontinued during the entire period of the six passes by the roller.After completion of the six passes, the quality of the image left on thesubstrate is evaluated as to density and color separation.

EXAMPLE IX The pigments are, as magenta, the phosphotungstomolybdic lakeof 3,6-bis(diethylamino)-9,2-carboxyphenyl xanthenonium chloride; ascyan, Monolite Fast Blue 6.5., the alpha form of metal-freephthalocyanine, C.I. No. 74100; and as yellow Algol Yellow GC, 1, 2, 5,6-d -(C, C -diphenyl)-thiazole-anthraquinone, C.I. No. 67300. Thistrimix, when exposed to a multicolored image, produces a full colorimage with good density and color balance.

EXAMPLE X The pigment suspension consists of a magenta pigment, thephosphomolybdic lake of3,6-bis(ethylamino)-2,7-dimethyl-9,2-carbethoxyphenyl xanthenoniumchloride; a cyan, pigment, Cyan GTNF, the beta form of copperphthalocyanine, C.I. No. 74160, and a yellow pigment, Indofast YellowToner, fiavanthrone, C.I. No. 70600. This trimix is exposed to amulticolored image and produces a full color image of good density.

EXAMPLE XI The pigment suspension consists of a magenta pigment, thephosphotungstomolybdic lake of 3,6-bis(diethylamino-9,2'-carbethoxyphenyl xanthenonium chloride; a cyan pigment, CyanBlue XR, the alpha form of copper phthalocyanine, and as a yellowpigment, 8,13-dioxodinaphtho(l,2 2',3')furan6-carbox-(3"-cyano-5"-methoxy)anilide prepared as described in copendingapplication Ser. No. 421,589, now abandoned, filed Dec. 28, 1964. Thistrimix is exposed to a multicolored image and produces a full colorimage of good density.

The compositions of the general formula given above are also useful inxerographic imaging systems. For use in such processes, xerographicplates may be produced by coating a relatively conductive substrate,e.g., aluminum or paper, with a dispersion of particles of thephotosensitive pigment of the above general formula in a resin binder.The pigment-resin layer may also be cast as a self-supporting film. Theplate formed may be both with or without an overcoating on thephotoconductive layer. As a third alternative to the above notedself-supporting layer and substrate supported layer, the photosensitivepigment-resin photoconductive layer may be used in the formation ofmultilayer sandwich configurations adjacent a dielectric layer, similarto that shown by Golovin et al., in the publication entitled A NewElectrophotographic Process, Effected by Means at Combined ElectretLayers, Doklady Akad. Nauk SSSR, vol. 129, No. 5, pp. 08- 1011,November-December 1959.

When it is desired to coat the pigmented resin film on a substrate,various supporting materials may be used. Suitable materials for thispurpose include aluminum, steel, brass, metalized or tin oxide coatedglass, semiconductive plastics and resins, paper and other convenientmaterials.

Any suitable dielectric material may be used to overcoat thephotoconductive layer. A typical overcoating is bichromated shellac.

Any suitable organic binder or resin may be used in combination with thepigment to prepare the photoconductive layer of this invention. In orderto be useful the resin used in the present invention should be moreresistive than about 10 and preferably more than 10 ohms per centimeterunder the conditions of xerographic use. Typical resins includethermoplastics such as polyvinyl chloride, polyvinyl acetates,polyvinylidene chloride, polystyrene, polybutadiene, polymethacrylates,polyacrylics, polyacrylonitrile, silicone resins, chlorinated rubber,and mixtures and copolymers thereof where applicable; and thermosettingresins such as epoxy resins including halogenated epoxy and phenoxyresins, phenolics, epoxyphenolic copolymers, epoxy ureaformaldehydecopolymers, epoxy melamine formaldehyde formaldehyde copolymers andmixtures thereof, where applicable. Other typical resins are epoxyesters, vinyl epoxy resins, tall-oil modified epoxies and mixturesthereof, where applicable. In addition to the above noted bindermaterials, any other suitable resin may be used if desired. Also, otherbinders such parafiin and mineral waxes may be used if desired.

The pigments may be incorporated in the dissolved or melted binder resinby any suitable means such as strong shear agitation, preferably withsimultaneous grinding. These include ball milling, roller milling, sandmilling, ultrasonic agitation, high-speed blending and any desirablecombination of these methods. Any suitable range of pigment-resin ratiosmay be used.

The pigment-resin-solvent slurry (or the pigment-resin melt) may beapplied to the conductive substrate by any of the well-known painting orcoating methods, including spraying, flow coating, knife coating,electrocoating, Mayer bar drawdown, dip coating, reverse foil coating,etc. Spraying in an electric fiield may be preferred for the smoothestfinish and dip coating for convenience in the laboratory. The setting,drying and/or curing steps for these plates are generally similar tothose recommended for films of the particular binder used for otherpainting applications. For example, pigment-epoxy plates may be cured byadding a cross-linking agent and stoving according to approximately thesame schedule as other baking enamels made with the same resins andsimilar pigments for painting applications. A very desirable aspect ofthese pigments is that they are stable against chemical decomposition atthe temperatures normally used for a wide variety of bake-on enamels,and therefore, may be incorporated in very hard glossy photoconductivecoatings, similar to automotive or kitchen appliance resin finishes.

The thickness of the photoconductive films may be varied from about 1 toabout 100 microns, depending on their required individaul purpose.Self-supporting films, for example, cannot usually be manufactured inthicknesses thinner than about 10 microns, and they are easiest tohandle and use in the 15 to micron range. Coatings, on the other hand,are preferably formed in the 5 to 30 micron range. For certaincompositions and purposes it is desirable to provide an overcoating;this should usually not exceed the thickness of the photoconductivecoating, and preferably not above one-quarter of the latter. Anysuitable overcoating material may be used, such as bichromated shellac.

This invention as it pertains to xerographic imaging processes will befurther described with reference to the following examples, whichdescribe in detail various preferred embodiments of the presentinvention. Parts, ratios, and percentages are by weight unless otherwiseindicated. Xerographic plates for use as in the following examples areprepared as follows: Mixtures using specific pigments and resin bindersare prepared by ball milling the pigment or a solution of a resinousbinder and one or more solvents until the pigment is well dispersed.This is done by adding the desired parts of resin solution in a suitablemixing vessel. A quantity of one-eighth inch steel balls are added andthe vessel is rotated for approximately one-half hour in order to obtaina homogeneous dispersion. The cooled slurry is applied onto an aluminumsubstrate with a wire drawdown and force dried in an oven for about 3minutes at about C. The coated sheets are dark rested for about 1 hourand then tested.

In the following examples, plates are tested as follows. The plate ischarged negative by corona discharge to about 400 volts and exposed to alight and shadow image. The plate is cascade developed using Xerox 1824developer. The powder image produced on the plate corresponds to theprojected image. The developed image may be then either fused to theplate or may be electrostatically transferred to a receiving sheet andthere fused. Where the image is transferred, the plate may be thencleaned of residual toner and may be reused as by the above describedprocess.

EXAMPLE XII The xerographic plate is prepared by initially mixing about2 parts of Lucite 2042, an ethylmethacrylate polymer, about 18 partsbenzene, and about 1 part of the phosphotungstomolybdic lake of3,6-bis(diethylamino)- 9, 2'-carboxyphenyl xanthenonium chloride. Thismixture is coated onto an aluminum substrate to a thickness of aboutmicrons and cured. The plate is then charged. exposed for about 60seconds to a light and shadow image using a Simmons Omega D3 enlargerequipped with a tungsten light source operating at 2950 K. colortemperature (illumination level incident on the plate is 2.8 footcandles as measured with a Weston illumination meter model No. 756), anddeveloped as above described. The image produced is heat fused directlyonto the plate. The image produced was found to be of satisfactoryquality.

EXAMPLE XIII The xerographic plate is prepared by initially mixing abinder and a solvent as in Example XII above with about 1 part of thephosphomolybdic lake of 3,6-bis(ethylamino)-2,7 dimethyl9,2'carbethoxyphenyl xanthenonium chloride. This mixture is coated on analuminum substrate to a thickness of about 8 microns and cured. Theplate is charged, exposed for about 45 seconds to a light and shadowimage using a Simmons Omega D3 enlarger equipped with a tungsten lightsource operating at 2950" K. color temperature (illumination levelincident on the plate is 2.8 foot candles as measured with a Westonillumination meter model No. 756) and developed. An image of goodquality results.

EXAMPLE X-IV The xerographic plate is prepared by initially mixing about3 parts of Lucite 2042 with about 100 parts benzene and about 10 partsof the phosphotungstomolybdic lake of 3,6 bis(diethylamino)9,2'carbethoxyphenyl xanthenonium chloride. The mixture is coated ontoan aluminum substrate to a thickness of about 8 microns and cured. Theplate is charged negative in the dark by means of a corona discharge toa potential of about 400 volts. The charged plate is exposed to a filmpositive for about 30 seconds by means of a high intensity, long wave,ultraviolet lamp (1680 microwatts/cm of 3660 A.U. radiation at adistance of 18 inches). The latent electrostatic image is developed bycascading Xerox 1824 toner over the plate. The powder image on the plateis electrostatically transferred to a receiving sheet and heat fused.The image on the receiving sheet is of good quality and corresponds tothe original. The plate is wiped clean of any residual toner and reusedas in the above manner.

Although specific components and proportions have been described in theabove examples relating to electrophoretic, and xerograp'hic imagingsystems other suitable materials, as listed above, may be used withsimilar results. In addition, other materials may be added to thepigment composition or to the pigment-resin compositions to synergize,enhance, or otherwise modify their properties. The pigment compositionsand/or the pigment-resin compositions of this invention may be dyesensitized, if desired, or may be mixed or otherwise combined with otherphotoconductors, both organic and inorganic.

Other modifications and ramifications of the present invention willoccur to those skilled in the art upon a reading of the presentdisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

1. The method of electrophoretic imaging comprising subjecting a layerof a suspension to an applied electric field between at least twoelectrodes, as least one of which is at least partially transparent andsimultaneously exposing said suspension to an image through saidpartially transparent electrode with activating electromagneticradiation whereby a pigment image made up of particles is formed on atleast one of said electrodes; said suspension comprising a plurality offinely divided photosensitive particles of at least one color, at leasta portion of said particles comprising a composition which is a lake ofa 3,6 bis(amino)-9,2'-carboxyphenyl xanthenonium salt.

2. The method of claim 1 wherein said lake is the phosphotungstomolybdiclake of 3,6-bis(diethylamino)- 9,2'-carboxyphenyl xanthenonium chloride.

3. The method of claim 1 wherein said lake is the barium salt of3,6-bis(diethylamino)-9,2-carboxyphenyl xanthenonium chloride.

4. The method of claim 1 wherein said lake is the phosphomolybdic lakeof 3,6-bis(ethylamino)-2,7-dimethyl-9,2'-carbethoxyphenyl xanthenoniumchloride.

5. The method of claim 1 wherein said lake is the barium salt of3,2-toluidine amino-6,2"-methyl-4"-Sulphophenylamino-9,2'"-carboxyphenylxanthene.

6. The method of electrophoretic imaging comprising subjecting a layerof a suspension to an applied electric field between at least twoelectrodes, at least one of said electrodes being a blocking electrode,and exposing said suspension to an image with activating electromagneticradiation whereby a pigment image made up of particles is formed on atleast one of said electrodes; said suspension comprising a plurality offinely divided photosensitive particles of at least one color, at leastone of said particles comprising a composition which is a lake of a3,6-bis(amino)-9,2'-carboxyphenyl xanthenonium salt.

7. The method of claim 6 wherein said lake is the phosphotungstomolybdiclake of 3,6-bis(diethylamino)- 9,2'-carboxyphenyl xanthenonium chloride.

8. The method of claim 6 wherein said lake is the barium salt of3,6-bis-(diethylamino)-9,2'-carboxyphenyl xanthenonium chloride.

9. The method of claim 6 wherein said lake is the phosphomolybdic lakeof 3,6 bis(ethylamino)-2,7-dimethyl-9,2'-carbethoxyphenyl xanthenoniumchloride.

10. The method of claim 6 wherein said lake is the barium salt of3,2-toluidine amino-6"-methyl-4"-sulphophenylamino-9,2'"-carboxyphenylxanthene.

11. The method of electrophoretic imaging comprising subjecting a layerof a suspension to an applied electric field between two electrodes, atleast one of which is at least partially transparent, said suspensioncomprising a plurality of finely divided particles of at least twodifferent colors in an insulating carrier liquid, the particles of eachcolor comprising a photosensitive pigment whose principal lightabsorption bands substantially coincides with its principalphotosensitive response, simultaneously exposing said suspension to alight image through said transparent electrode and then separating saidelectrodes whereby a pigment image is formed on the surface of at leastone of said electrodes; the particles of one color comprising acomposition which is a lake of a 3,6-bis(amino)-9,2'-carboxyphenylxanthenonium salt.

12. The method of electrophoretic imaging comprising subjecting a layerof a suspension to an applied electric field between two electrodes, atleast one of which is a blocking electrode, said suspension comprising aplurality of finely divided particles of at least two different colorsin an insulating carrier liquid, the particles of each color comprisinga photosensitive pigment whose principal light absorption bandssubstantially coincides with its principal photosensitive response,simultaneously exposing said suspension to a light image and thenseparating said electrodes whereby a pigment image is formed on thesurface of at least one of said electrodes; the particles of one colorcomprising a composition which is a lake of a 3,6-bis(amino)-9,2-carboxyphenyl Xanthenonium salt.

13. A xerographic plate comprising a photoconductive layer comprising abinder material and a composition which is a lake of a3,6-bis(amino)-9,2-carboxyphenyl Xanthenonium salt.

14. The plate of claim 13 wherein said lake is the phosphomolybdic lakeof 3,6-bis(ethylamino)-9,2'-carboxyphenyl xanthenonium chloride.

15. The plate of claim 13 wherein said lake is thephosphotungstomolybdic lake of 3,6-bis(diethylamino)- 9,2-carboxyphenylxanthenonium chloride.

16. The plate of claim 13 wherein said lake is the barium salt of3,6-bis(diethylamino)-9,2'-carboxyphenyl xanthenonium chloride.

17. The plate of claim 13 wherein said lake is the phosphomolybdic lakeof 3,6-bis(ethylamino)-2,7-di methyl-9,2'- carbethoxyphenyl xanthenoniumchloride.

18. A process for forming a latent xerographic image on aphotoconductive layer comprising a photoconductive pigment in an organicbinder, which comprises electrostatically charging said layer andexposing said layer to a pattern of activating electromagneticradiation; said photoconductive pigment comprising a composition whichis a lake of a 3,6-bis(amino)-9,2-carboxyphenyl xanthenonium salt.

19. An imaging process which comprises the steps of providing ap'hotoconductive layer comprising a photo conductive pigment in anorganic binder, uniformly electrostatically charging said layer,exposing said layer to a pattern of activating electromagnetic radiationand contacting said layer with electroscopic marking particles wherebysaid particles are held to said layer in pattern configuration; saidphotoconductive pigment comprising a composition which is a lake of a3,6-bis(amino)-9,2'- carboxyphenyl xanthenonium salt.

References Cited UNITED STATES PATENTS 1,006,738 10/1911 Emmerich 2603362,149,992 3/1939 Fonda 260-336 2,758,939 8/1956 Sugarman 96--1.42,940,847 6/1960 Kaprelian 96-4 3,247,081 4/ 1966 Reithel 204-183,367,946 2/1968 Stryker 260336 HOWARD S. WILLIAMS, Primary Examiner.

E. ZAGARELLA, Assistant Examiner.

US. Cl. X.R.

1. THE METHOD OF ELECTROPHORETIC IMAGING COMPRISING SUJECTING A LAYER OFA SUSPENSION TO AN APPLIED ELECTRIC FIELD BETWEEN AT LEAST TWOELECTRODES, AS LEAST ONE OF WHICH IS AT LEAST PARTIALLY TRANSPARENT ANDSIMULTANEOUSLY EXPOSING SAID SUSPENSION TO AN IMAGE THROUGH SAIDPARTIALLY TRANSPARENT ELECTRODE WITH ACTIVATING ELECTROMAGNETICRADIATION WHEREBY A PIGMENT IMAGE MADE UP OF PARTICLES IS FORMED ON ATLEAST ONE OF SAID ELECTRODES; SAID SUSPENSION COMPRISING A PLURALITY OFFINELY DIVIDED PHOTOSENSITIVE PARTICLES OF AT LEAST ONE COLOR, AT LEASTA PORTION OF SAID PARTICLES COMPRISING A COMPOSITION WHICH IS A LAKE OFA 3,6-BIS(AMINO)-9,2''-CARBOXYPHENYL XANTHENONIUM SALT.